PIPIDAE

Candioti, M. Florencia Vera, 2007, Anatomy of anuran tadpoles from lentic water bodies: systematic relevance and correlation with feeding habits, Zootaxa 1600, pp. 1-175 : 119-124

PIPIDAE

Xenopus laevis . This species has been long studied; previous literature includes papers by Ridewood (1897; 1898), Ramaswami (1941), Weisz (1945), Gradwell (1971), Seale and Wassersug (1979), Wassersug and Hoff (1979; 1982), Satel and Wassersug (1981), Trueb and Hanken (1992), and Haas (2001; 2003), among other researchers.

Chondrocranium and hyobranchial skeleton (N = 5, stage 31. Fig. 69). The chondrocranium of these larvae represents 56% of the body length. The maximum width is at the plane of the muscular process of the palatoquadrate and the processus lateralis posterior of the palatoquadrate. The ethmoid region is represented by a broad plate, homologous to the suprarostral cartilage and the trabecular horns of other tadpoles ( Sokol 1975; Swart & De Sá 1999). This plate attenuates laterally and joins with a thin anterior process of the palatoquadrate, the processus cornu quadratus lateralis, constituting the tentacular cartilage. The cranial floor is completely cartilaginous and the carotid and craniopalatine foramina are visible and small. In the posterior margin of the cranial floor, the notochordal canal extends 11% of the chondrocranium length. In the lateral walls of the chondrocranium, the orbital cartilages are completely formed and show the optic, oculomotor, trochlear and prootic foramina. The chondrocranium is open dorsally through the frontoparietal fenestra, which is lined by the taeniae tecti marginales and anteriorly by the tectum anterius. Two longitudinal channels, the olfactory channels, diverge anterolaterally from the tectum anterius. The otic capsules are quadrangular and large, occupying nearly 30% of the chondrocranium total length. The crista parotica is well-developed, located anterolaterally to the otic capsule, and it is continuous with a flat flange of cartilage that borders the lateral and posterolateral margin of the capsule. The fenestra ovalis (39% of the capsule length) is located ventrolaterally on each otic capsule. The otic capsules are dorsally joined by the tectum synoticum. In the palatoquadrate, the articular process is very short. Laterally, the thin processus cornu quadratus lateralis arises, and medially, there appear a wide process, the processus cornu quadratus medialis. The muscular process is weakly developed. The subocular bar is interrupted approximately at half its length: the anterior part encloses the anterior portion of the subocular fenestra, and the posterior part arises from the long, flat, rectangular, posterolaterally directed processus lateralis posterior. The palatoquadrate attaches to the braincase via three points: the broad quadratocranial commissure, the ascending process, with a high attachment to the neurocranium, and the larval otic process, which joins the processus lateralis posterior and the otic capsule. The lower jaw includes the Meckel’s and infrarostral cartilages. Meckel’s cartilages are elongate, curved, without processes, and articulate with the fused, indistinct infrarostral cartilages. A remarkable feature of the hyobranchial skeleton of this species is the presence of craniobranchial commissures, which join the crista parotica of the neurocranium with the lateral margins of the branchial basket. The ceratohyals are elongate and have a thin, acuminate, medially directed anterior process, a low, wide and rounded anterolateral process, a robust lateral process, and a long, thin posterior process, continuous with the basibranchial; the articular condyle is a rounded protuberance visible from a dorsal view. The basihyal is absent and the pars reuniens and the basibranchial are fused forming a median element that lies in a passage formed by a groove of each ceratohyal posterior process. The basibranchial is posteriorly fused to the hypobranchial plates. The urobranchial process is absent. The ceratobranchials are fused to the hypobranchial plates and constitute a large, voluminous branchial basket. Proximal and terminal commissures I-III are present, joining all the ceratobranchials anterior and distally. The ceratobranchials have numerous lateral projections, and dorsally, all the filter plates corresponding to each ceratobranchial are chondrified. Spicules are absent.

Musculature (N = 5, stage 31. Table 20 and Fig. 70). Twenty-four muscles are present in this species.

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Levator mandibulae longus anterior, lateral surface of the subocular bar – ventral it is very thin, formed of a few fibers, profundus surface of the tentacle cartilage, near the junction of and it runs parallel to the m. l. m. l.

the tentacle and the distal tip of the suprarostral superficialis until it diverges toward its

cartilage insertion

Levator mandibulae internus anterior, medial surface the subocular bar – lateral it is scarcely developed, formed of a edge of Meckel’s cartilage few fibers

Levator mandibulae externus anterior, medial surface of the muscular process – the mandibular branch of the

dorsal, lateral region of the Meckel’s cartilage trigeminal nerve (V 3) runs dorsally to

this muscle; there is no division into

mm. l. m. e. superficialis and

profundus

Levator mandibulae articularis anterior, dorsal surface of the palatoquadrate – lateral it is a short, oblique muscle

edge of Meckel’s cartilage

Orbitohyoideus anterior, dorsal margin of the muscular process –

lateral edge of the ceratohyal

Quadratoangularis ventral surface of the palatoquadrate – lateral edge of in the literature about pipids, these two Meckel’s, cartilage sharing the point of origin with muscles appear referred to as a single

the m. hyoangularis muscle, the m. quadratohyoangularis

Hyoangularis dorsal surface of the ceratohyal – lateral edge of

Meckel’s cartilage

Interhyoideus ventral surface of the lateral process of the ceratohyal it is well-developed, formed of parallel – median aponeurosis fibers, transversally disposed

Geniohyoideus posterior, ventral surface of the infrarostral – it is very thin, formed of 4-5 fibers proximal point of the ceratobranchial II

Levator arcuum branchialium I- ventral surface of the posterior region of the these three muscles are very close, and III subocular bar, ventral surface of the processus it is impossible to tell them apart

lateralis posterior, and ventrolateral surface of the otic

capsule – lateral surface of ceratobranchials I, III and

III

Levator arcuum branchialium posterolateral surface of the otic capsule – terminal

IV commissure III and medial, ventral surface of the

ceratobranchial IV

Dilatator laryngis posterolateral surface of the otic capsule – arytenoid

cartilage

Constrictor branchialis II proximal point on the ceratobranchial II – terminal

commissure I

Constrictor branchialis III proximal point on the ceratobranchial III – distal it runs on the anterior margin of the point on the ceratobranchial III ceratobranchial III

Subarcualis rectus I posterior, medial margin of the ceratohyal – proximal it is formed of a short, single slip of part of the ceratobranchial I fibers

Subarcualis rectus II-IV proximal point on the ceratobranchial III, medial to this muscle resembles the mm.

the former muscle – terminal commissure III constrictor branchiales in orientation,

due to its far lateral origin, without any

attachment on the medial

ceratobranchial IV

Subarcualis obliquus ceratobranchial II – median aponeurosis

Diaphragmatobranchialis peritoneum – distal edge of the ceratobranchial III

Rectus cervicis + Rectus ceratobranchial III – pelvic griddle fibers of these two muscles are abdominis continuous, and form two single layers on each side of the abdomen

Oral apparatus and buccopharyngeal cavity (N = 2, stage 31. Fig. 71). The mouth is terminal with a wide oral slit devoid of papillae and keratinized structures. Gape width reaches 32% of the body length. Two thin tentacles arise from the buccal commissures. The buccal roof is not pigmented and devoid of any papillae or pustulation. The choanae are large, subcircular, and anteriorly located. On both sides of the roof, there appear three paired pad-like structures, supposed to be homologous to the dorsal velum of other species. Conspicuous secretory pits appear in the dorsal vela, and the tissue surrounding them. The buccal floor is also short and smooth, with only a small pair of short papillae on the anterior margin of the ceratohyals. A free valve-like flap is absent and the secretory ridges, that in other tadpoles are characteristic of the ventral velum, develop in a structure named “pharyngobranchial tract” by Weisz (1945). This structure includes a thick central band along the dorsal edge of the hypobranchial plate, and triangular projections out along the crest of each filter plate. The secretory ridges run parallel to the contour of the pharyngobranchial tract. Secretory pits appear on the anterior, central region of the pharyngobranchial tract.

Gut content (N = 7, stages 30–31. Tables 21 and 22). As in microhylids, distinctive mucous cords appear inside the digestive tract. These cords are, however, far thinner, with a diameter ≅ 0.3 mm ( Fig. 72). Entangled in these mucous strings, there appear unicellular chlorophytes as small as 0.005 mm (which represents <1% of the tadpole size, accumulating almost 2% of the total food volume) and large cladocerans (3%–6% of the tadpole size; 97.6% of the total volume).